The present invention relates to a drive controller for a self-commutated converter, and more particularly to a drive controller with a switched control circuit for the converter valves that can be dynamically and cyclically tested without interrupting service.
Great care must be exercised when using electric drives in industrial automation applications, for example with numerically controlled machine-tools and robots, to protect men and machine in the best possible manner. The electrical machine or the motor should be prevented from performing dangerous movements even when a single error occurs, by implementing a “safe stop” function for the motor. This function is typically initiated depending on the operating mode, e.g., before a protective door is opened.
The “safe stop” function is implemented by disconnecting the electric power in two places, for example, by also disconnecting the motor. It is generally accepted to separately disconnect the lower and/or upper converter valves of a self-commutated converter employing a bridge circuit.
A “safe stop” function can be implemented by “safely” blocking the control signals to the converter valves, which is referred to in the art also as “pulse inhibitor”, or to disconnect all converter valves.
The term “safely” is intended to indicate that the regulatory requirements imposed or suggested by the professional organizations or regulatory bodies for occupational safety are satisfied.
A conventional drive controller of this type is known from the German patent DE 100 59 173, as shown in detail in FIG. 1. The self-commutated converter W has two half-bridges with converter valves T1, T3, T5, and T2, T4, T6, respectively. The drive controller has a separate control circuit for each half-bridge. Of the control circuits, only the associated opto-couplers OK1, OK3, OK5 for the upper half-bridge, and OK2, OK4, OK6 for the lower half-bridge are shown in FIG. 1. The anodes of the photodiodes of the opto-couplers OK1, OK3, OK5 and OK2, OK4, OK6 are electrically connected with respective supply voltages SV1 and SV2, whereas the cathodes are electrically connected with corresponding pulse inhibiting circuits I1 and I2 via resistors RS1, RS3, RS5, and RS2, RS4, RS6, and forward-biased diodes DS1, DS3, DS5, and DS2, DS4, DS6 connected downstream of the resistors. The function “safe stop” is “reliably” selected via the two signals SH1 and SH2 via the external periphery of two-channel safety switches (not shown). The signal SH1 is applied to the pulse inhibiting circuit I1 and the signal SH2 is applied to the pulse inhibiting circuit I2. The systems I1 and I2 test the input signals for quality by exchanging information via a communications link KOMM, and in the event of a discrepancy inhibit the pulses by means of the switches S1 and S2 and the drive unit ST. The respective supply voltages SV1 and SV2 are present at corresponding outputs of pulse inhibiting paths IP1 and IP2. Each of the pulse inhibiting paths IP1 and IP2 includes a switch S1 and S2, respectively, with each of the switches S1 and S2 receiving control signals from a corresponding one of the pulse inhibiting circuits I1 and 12. The pulse inhibiting path IP1 and/or IP2 is equivalent to a disconnectable power supply which is disconnected when a “safe stop” is triggered. The output side of each pulse inhibiting path IP1 and IP2 is connected to an associated pulse inhibiting circuit I1, I2 via a diagnostic line which includes a decoupling diode, supplying corresponding diagnostic signals SV1_Diag and SV2_Diag to the pulse inhibiting circuits I1 and I2.
The opto-couplers OK1 to OK6 are arranged between the control electronics, which includes a microprocessor and a driver for each converter valve T1 to T6 of the self-commutated converter W. Transformers can also be used instead of the opto-couplers OK1 to OK6. This type of signal transmission device, i.e. opto-coupler and/or transformer, eliminates the effect of interference voltages on the microprocessor of the control electronics.
The function “safe stop” is implemented by a pulse inhibitor which is used to switch off the converter valves T1 to T6 of the inverter W during normal operation or when a fault is detected. Preferably, the supply voltage SV1 for the opto-couplers OK1, OK3, OK5 for the upper bridge arm of converter valves, which is derived from an external voltage SV, is interrupted by switch S1 (either a mechanical or an electronic switch) by applying a signal IL1 from the pulse inhibiting circuit 11. Another supply voltage SV2 for the opto-couplers OK2, OK4, OK6 for the lower bridge arm is interrupted by switch S2 (either a mechanical or an electronic switch) by applying a signal IL2 from the pulse inhibiting circuit 12, as well as by blocking the pulses in the control set ST.
The operation of the two pulse inhibiting paths IP1 and IP2 with the switches S1 and S2 can be checked cyclically and dynamically, for example each time after the supply voltage is switched on. For this purpose, the pulse controller I1 reads the supply voltage SV1 from the diagnostic signal SV1_Diag measured downstream of the switch S1 after the switch S1 has been activated, and the supply voltage SV2 from the diagnostic signal SV2_Diag measured downstream of the switch S2 after the switch S2 has been activated. Even if one of the pulse controllers I1 and I2 fails, the other correctly functioning pulse inhibiting controller I2 or I1 can still respond, since the aforedescribed forced dynamical operation can detect even so-called dormant errors.
Disconnectable paths have to be tested for errors, since the probability of a component failure is never zero. As mentioned above, the function “safe stop” requires two redundant disconnectable paths which are checked at predefined test intervals, for example every eight hours. This guarantees the required protection against single faults. However, the operation of the device must be interrupted for the test, which makes more frequent tests of the disconnectable paths impractical.
It is also possible to connect to switches electrically in parallel, in which case the parallel switches are decoupled by decoupling diodes. The functionality of these switches can be checked during operation by alternatingly turning the switches on and off. Moreover, a circuit for temporarily maintaining a DC voltage can be connected downstream of the two switches, so that the voltage of the control circuit(s) connected downstream is unaffected when the switches are briefly opened. Accordingly, the state of each switch can be tested in a forced dynamical operation without service interruption.
It would therefore be desirable and advantageous to improve the disconnectable voltage supplies of conventional drive controllers by obviating prior art shortcomings and providing a less complex switch configuration, so that the switches of converters can be tested more frequently and at arbitrary time intervals without service interruption.